1. Field of the Invention
This invention relates to a method for removing water from a produced crude oil stream containing droplets of water suspended therein in the form of an emulsion by passing the water-in-oil emulsion through a water saturated hydrophilic coalescing media such as sand or crushed quartz whereby the droplets of water are coalesced into a water phase which can be easily separated from the oil by gravity.
2. Background of the Invention
In oil fields, water usually is produced with crude oil. The crude oil must generally be free of water before it can be sold and transported in pipelines. The complexity of separating mixtures of water and oil depends upon the physical form of the water. Where the mixture has only "free" water, the water will separate readily from the oil because of the differences in gravities of the water and oil. This type of separation presents no problem other than providing a vessel in which water-oil phase separation can occur. However, the water can be dispersed throughout the oil in very minute particles, usually with diameters less than 25 microns. This mixture may be termed an emulsion and is very difficult to separate into water and oil phases.
The breaking of emulsions in which water is dispersed in the continuous crude oil phase requires performing certain functions. Initially, the interfacial protective film surrounding the dispersed water within the emulsion must be weakened or destroyed. Then, the particles of water must coalesce into droplets of water which can undergo settling through the effects of gravity. Thereafter, the coalesced droplets of water are separated a a water phase from the oil phase.
Breaking of emulsions may be achieved at considerable expense through the use of free water knockouts, chemical injection, heater treaters, chemical-electric treaters, and other similar equipment all of which are very expensive. Those methods which use heat are difficult and costly to maintain, as well as needing large quantities of fuel. Generally, the methods for breaking a water-in-oil emulsion usually employ a combination of these treatments. In many instances, chemical demulsifiers may be employed for assisting in the breaking of the protective film which surrounds the dispersed water. The demulsifiers are added to the emulsion to counter-act the effects of the emulsifiers which provide the stability of the dispersed water particles in the continuous oil phase. The demulsifier is uniformly distributed throughout the emulsion so as to be present at all interfaces between the water and oil before the emulsion is processed in a treating facility.
A large part of the cost of oil production, both capital and expense, goes toward treating oil field emulsions. Water must be removed from the crude prior to selling or shipping it. Allowable water content varies from under one percent up to three percent. To reach these values, chemical plus heat treatments are normal, with dilution and electrical methods used with more difficult emulsions. Even more-difficult-to-break emulsions, as from in-situ combustion projects, may require a second-stage treatment similar to the first to reduce water content to that required for shipment or sales. Chemical costs run high; purchase and maintenance of heater treaters is expensive; much fuel is burned. Most producing areas incur these costs.
U.S. Pat. No. 3,489,680 describes a method for breaking a water-in-oil emulsion into water and oil phases using a hydrocyclone in conjunction with a hydrophilic coalescing membrane.
German Patent No. 257,194 issued Feb. 26, 1913, discloses a process for separating water from crude oil by mixing the water containing crude oil with sharp-grained materials such as sharp sand, fine splinters of glass, iron chips or the like. If necessary, heat and simultaneous use of an air stream as a stirring mechanism may be employed. Mixing may also occur in a heated filter filled with sharpgrained material.
The present invention provides an effective and economical method for removing water from a natural emulsion of reservoir water in produced reservoir crude oil by passing the emulsion through a water saturated hydrophilic coalescing media such as sand or crushed quartz whereby the water droplets are coalesced into a water phase capable of separation from the crude oil by gravity.